Field of the Invention
The invention relates to a method for driving an integrated power output stage for switching loads connected to terminals of a voltage source. The invention also relates to a device for carrying out this method.
U.S. Pat. No. 5,315,174 discloses such a device for driving a load using a power output stage, in which a steepness of switching edges of the power transistor connected in series with the load to the terminals of a voltage source can be adjusted, on the basis of external control signals (which can also be stored), to be either steep at first and then shallower, or just shallow.
U.S. Pat. No. 5,568,081 discloses a device for driving a power output stage, in which the steepness of the turn-on and turn-off edges of the power transistors can be adjusted on the basis of external control signals. In addition, during periods of the output signal when the di/dt derivative for output current against time is large, shallow turn-on and turn-off edges can be chosen, and during periods of the output signal when the di/dt derivative for output current against time is small, steep turn-on and turn-off edges can be chosen.
U.S. Pat. No. 5,617,051 discloses a device for limiting voltage overshoot, in which the change or rate of change in the output voltage is measured. If predetermined values are exceeded, the output is fed back to the drive circuit so that the overshoot behavior is reduced as a result of the switching edges being flattened.
Power output stages are used in large numbers particularly in the field of engine control in motor vehicles. Depending on the application, the individual loads are driven sporadically, at a fixed driving frequency or depending on engine speed, with switching times which have to be adhered to more or less exactly. The more precisely the switching times have to be adhered to, the steeper the rising and falling edges required for the output stage switches directly switching the load; for less time-critical applications, freewheeling diodes are connected in parallel with the loads.
If the loads are driven on the basis of engine speed, in which case exact turn-on times, for example for fuel injection or ignition, are usually required, then the interference spectrum produced by the steep edges of the switching signals has a broad bandwidth. Loads driven at a fixed frequency form a fixed interference frequency and are therefore more critical.
Each type of driving for these loads requires specially matched power output stages. The large number of power output stages required results in that integrated multiple drivers are used, e.g. quadruple or octuple drivers, and, in the near future, ICs with even more drivers as a result of higher integration density, which need to be matched to the particular application using external components, at high cost. In this context, it is common practice to make the switching edges of the power switches just as steep as the application requires to keep the radiated interference as low as possible.